Evaluation of the Potential Release Risk of Internal N and P from Sediments—A Preliminary Study in Two Freshwater Reservoirs in South China

Peng Cheng,Qingman Li,Yang Jiao,Xuezhi Zhang,Sen Gu,Xu Bao

doi:10.3390/w14040664

Abstract

Growing evidence has demonstrated the influence of internal nitrogen (N) and phosphorus (P) on harmful algae blooms in eutrophic freshwater ecosystems. However, the main controlling factors for internal N and P release risks, and whether these factors vary as environmental conditions change, remains poorly understood. We evaluated potential release risks of N and P from sediments in two freshwater reservoirs in Beihai City, southern China, by evaluating apparent nutrient fluxes during simulated static incubation experiments at two temperatures (15 °C and 25 °C). Sediments were analyzed to determine their basic properties as well as N and P fractions. Results showed that the main controlling factors of the apparent fluxes in dissolved total P, soluble reactive P, total N, and ammonium were related to sediment adsorption properties, redox properties, and microbial-mediated properties (e.g., water-extractable P, total inorganic N, redox-sensitive P, total organic carbon, organic P). The primary controlling factors for apparent N and P fluxes were dependent on the form of N and P and changed with temperature. The results suggest that care should be taken when simply using total N and P contents in sediments to evaluate their internal nutrient release risks.

Highlights

Human activities have delivered excess nutrients to aquatic ecosystems, which has caused widespread eutrophication of freshwater lakes and reservoirs [1,2,3]
Sediment Total organic carbon (TOC), Water extractable P (WEP), and Organic P (OP) contents and Eh and pH values showed no obvious trend as a function of sediment depth (Figure S2)
The results of the present study indicated that temperature had a significant influence on apparent fluxes of N and P from the reservoir sediments, as mean apparent fluxes of total P (TP), soluble reactive P (SRP), total N (TN), and NH4 -N in the simulated static incubations were significantly larger at 25 ◦ C than at 15 ◦ C (Figures 4 and 5)

Summary

Introduction

Human activities have delivered excess nutrients to aquatic ecosystems, which has caused widespread eutrophication of freshwater lakes and reservoirs [1,2,3]. Numerous management efforts have been made to reduce the loading of external nutrients into freshwater bodies [8,11] Such reductions in external nutrient loading are reported to be rapidly effective in controlling freshwater eutrophication in certain lakes, but not in many others, due to internal sediment loading [12,13,14,15]. Due to this internal loading, eutrophication can persist for 5–15 years after external nutrient inputs have been reduced [16,17]

Methods

Results

Discussion

Conclusion